The present invention relates to a positive photoresist composition used in an ultramicrolithography process, e.g., for the production of VLSI and high capacity microchips, or other photofabrication processes. More specifically, the invention relates to a positive photoresist composition exhibiting satisfactory exposure margin and edge roughness.
Recently, the degree of integration of integrated circuits is becoming much higher, and the processing for superfine patterns having a line width of half micron or less is beginning to be required in the production of semiconductor substrates for VLSI and the like. In order to meet such a requirement, the wavelengths used in an exposure apparatus for photolithography are becoming shorter, and nowadays the use of far ultraviolet light having shorter wavelength, excimer laser beams (XeCl, KrF, ArF, etc.), is being investigated.
On of the resists for use in this wavelength region is a chemically amplified resist.
In general, the chemically amplified resist is roughly divided into three types, the so-called two-component, two point five-component and three-component types. The chemically amplified resist of two-component type is a combination of a compound which generates an acid by photolysis (hereinafter, referred to as a xe2x80x9cphoto-acid generatorxe2x80x9d) with a binder resin. The binder resin is a resin which has, in a molecule, a group capable of being decomposed by the action of an acid to increase the solubility of resin in an alkaline developing solution (which are sometimes referred to as xe2x80x9cacid-decomposable groupxe2x80x9d). The resist of two point five-component type further contains a low molecular weight compound having an acid-decomposable group in addition to the above two components. The resist of three-component type contains a photo-acid generator, an alkali-soluble resin and the above low molecular weight compound.
The chemically amplified resist is a photoresist suitable for exposure to ultraviolet light or far ultraviolet light. Further, it is necessary for the resist to satisfy the required characteristics in the practical use. As photoresist compositions for the ArF excimer light source, the combinations of (meth)acrylic resins showing less absorption of light than partially hydroxylated styrene resins with compounds which generate acids upon exposure are proposed in, e.g., JP-A-7-199467 and JP-A-7-252324 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d). Specifically, JP-A-6-289615 discloses a resin whose oxygen atom of the carboxyl group of the acrylic acid is bonded to a tertiary carbon-organic group through ester linkages.
Further, JP-A-7-234511 discloses an acid-decomposable resin containing acrylate esters and fumarate esters as repeating units. However, those resins only provide insufficient pattern profile and adhesiveness to a substrate and thus, they are not successful in ensuring satisfactory performances.
Furthermore, a resin where an alicyclic hydrocarbon moiety is introduced for the purpose of imparting dry etching resistance is proposed.
JP-A-9-73173, JP-A-9-90637, and JP-A-10-161313 describe resist materials which comprises acid-sensitive compounds containing alkali-soluble groups protected by alicyclic group-containing structures and structural units making the alkali-soluble groups alkali-soluble through the elimination of the alkali-soluble groups by an acid.
Moreover, JP-A-9-90637, JP-A-10-207069, and JP-A-10-274852 describe resist compositions containing acid-decomposable resins having specific lactone structures.
In the lithography process for device production where the wavelength of an irradiation for exposure lies in conventional UV or deep UV region, i.e., from about 240 nm to about 370 nm, resist materials containing polymers having ethylenic or aromatic unsaturation are generally use.
However, such resist materials are mostly unsuitable for the process of exposure with an irradiation of 193 nm. The reason is that a carbon-carbon double bond absorbs the irradiation of this wavelength. As a result, the resist materials used in the lithography process where the wavelength of an irradiation for exposure is 248 nm or higher cannot be used in the process where an irradiation for exposure having a wavelength of 193 nm is used.
Since the lithography process for producing devices under a design rule of 0.18 xcexcm and 0.13 xcexcm or less uses a light having a wavelength of 193 nm as the irradiation for exposure, a resist polymer containing little ethylenic unsaturation is desired. The materials described in JP-A-10-10739 and JP-A-10-307401 have improved transparency toward a light having a wavelength of 193 nm but is not so highly sensitive, and they are unsatisfactory in performance as resists for the lithography for use in design rule of 0.13 xcexcm or less, for example, insufficient resolving power.
JP-A-10-130340 discloses a chemically amplified resist containing a terpolymer having a specific repeating unit with a norbornene structure at the main chain.
Further, JP-A-2000-26446 provides a resist for ArF exposure having an excellent resolution by use of a polymer containing a (meth)acrylate having a lactone structure as the repeating unit.
Furthermore, an attempt to improve transparency toward a light having a short wavelength, dry etching resistance and resolution by use of a resin having a bridged alicyclic skeleton where at least one carbon atom is bonded to an oxygen atom through a double bond is described in JP-A-2000-122294.
However, such chemically amplified resists have possessed problems of line edge roughness and occurrence of defects at developing. The line edge roughness means that an edge at a substrate interface shows unevenness at overhead view of a pattern because a line pattern of the resist and the edge moves irregularly in the perpendicular direction against the line direction owing to the characteristic property of the resist. This unevenness causes inhibition of pattern resolving power and deterioration of electric property through transcription in etching process where the resist is used as the mask, and therefore, the process yield is lowered. In particular, as the size of resist pattern decreases to quarter micron or less, the demand for improving line edge roughness has been increasing but the guideline for the improvement has hardly been disclosed.
Further, there also exists a necessity for improving exposure margin. The exposure margin herein means a phenomenon of changing the line width of the resulting pattern with the change of light exposure.
Accordingly, an object of the invention is to provide a positive photoresist composition exhibiting reduced line edge roughness and occurrence of developing defects.
Another object of the invention is to provide a positive photoresist composition exhibiting an improving effect on exposure margin, especially exposure margin of an isolated line, i.e., small variation of line width of an isolated line when light exposure is changed.
As a result of the extensive studies of constituent materials for positive resist compositions of chemically amplified type, the present inventors have found that the above objects of the invention can be attained by use of an acid-decomposable resin having a repeating unit having a particular structure, thereby achieving the present invention.
Namely, the above objects are attained by the following constitutions.
(1) A positive photoresist composition comprising:
(A) a resin which contains a repeating unit represented by the following general formula (I) and a repeating unit represented by the following general formula (II), and whose dissolving rate toward an alkaline developing solution is increased by the action of an acid, and
(B) a compound which generates an acid upon irradiation with an actinic ray or a radiation, 
wherein in the formula (I), Rn1 to Rn4 each represents a hydrogen atom or an alkyl group which may have one or more substituents, and a is 0 or 1; and in the formula (II), R1 represents a hydrogen atom or a methyl group, W represents one group or a combination of two or more groups each selected from the group consisting of a single bond, an alkylene group, an ether group, a thioether group, a carbonyl group, and an ester group, Ra, Rb, Rc, Rd, and Rd each independently represents hydrogen atom or an alkyl group having 1 to 4 carbon atoms, m and n each independently represents an integer of 0 to 3, and m+n is from 2 to 6.
(2) A positive photoresist composition comprising:
(A1) a resin which contains a repeating unit represented by the following general formula (I), a repeating unit represented by the following general formula (NII) and a repeating unit having a group represented by any of the following general formulae (I-1) to (I-4), and whose dissolving rate toward an alkaline developing solution is increased by the action of an acid, and
(B) a compound which generates an acid upon irradiation with an actinic ray or a radiation, 
wherein in the formula (I), Rn1 to Rn4 each represents a hydrogen atom or an alkyl group which may have one or more substituents, and a is 0 or 1;
in the formula (NII), Rn5 represents a hydrogen atom or a methyl group; A represents one group or a combination of two or more groups each selected from the group consisting of a single bond, an alkylene group, a cycloalkylene group, an ether group, a thioether group, a carbonyl group and an ester group; W represents a group represented by xe2x80x94C(Rna)(Rnb)(Rnc) or a group represented by xe2x80x94CH(Rnd)xe2x80x94Oxe2x80x94Rne, wherein Rna, Rnb, and Rnc each represents a linear or branched alkyl group having 1 to 20 carbon atoms or an alicyclic hydrocarbon group which may have a halogen atom, an alkyl group, an alkoxy group, an alkoxycarbonyl group, an acyl group or an acyloxy group as a substituent, provided that Rna and Rnb may be bonded to each other to form an alicyclic ring together with the carbon atom to which the groups are commonly attached and, in this case, Rnc is an alkyl group having 1 to 4 carbon atoms, Rnd represents a hydrogen atom or an alkyl group, Rne represents a linear or branched alkyl group having 1 to 20 carbon atoms or an alicyclic hydrocarbon group which may have a halogen atom, an alkyl group, an alkoxy group, an alkoxycarbonyl group, an acyl group or an acyloxy group as a substituent;
In the general formulae (I-1) to (1-4), R1 to R5 may be the same or different, and each represents a hydrogen atom, or an alkyl group, a cycloalkyl group or an alkenyl group which may have one or more substituents, and two of R1 to R5 may be bonded to each other to form a ring.
(3) A positive photoresist composition comprising:
(A2) a resin which contains a repeating unit represented by the following general formula (I), a repeating unit represented by the following general formula (NII) and a repeating unit represented by the following general formula (Ixe2x80x2), and whose dissolving rate toward an alkaline developing solution is increased by the action of an acid, and
(B) a compound which generates an acid upon irradiation with an actinic ray or a radiation, 
wherein in the formula (I), Rn1 to Rn4 each represents a hydrogen atom or an alkyl group which may have one or more substituents, and a is 0 or 1;
in the formula (NII), Rn5 represents a hydrogen atom or a methyl group; An represents one group or a combination of two or more groups each selected from the group consisting of a single bond, an alkylene group, a cycloalkylene group, an ether group, a thioether group, a carbonyl group and an ester group; W represents a group represented by xe2x80x94C(Rna)(Rnb)(Rnc) or a group represented by xe2x80x94CH(Rnd)xe2x80x94Oxe2x80x94Rne, wherein Rna, Rnb, and Rnc each represents a linear or branched alkyl group having 1 to 20 carbon atoms or an alicyclic hydrocarbon group which may have a halogen atom, an alkyl group, an alkoxy group, an alkoxycarbonyl group, an acyl group or an acyloxy group as a substituent, provided that Rna and Rnb may be bonded to each other to form an alicyclic ring together with the carbon atom to which the groups are commonly attached and, in this case, Rnc is an alkyl group having 1 to 4 carbon atoms, Rnd represents a hydrogen atom or an alkyl group, Rne represents a linear or branched alkyl group having 1 to 20 carbon atoms or an alicyclic hydrocarbon group which may have a halogen atom, an alkyl group, an alkoxy group, an alkoxycarbonyl group, an acyl group or an acyloxy group as a substituent; and
in the general formulae (Ixe2x80x2), A represents one group or a combination of two or more groups each selected from the group consisting of a single bond, an alkylene group, a cycloalkylene group, an ether group, a thioether group, a carbonyl group and an ester group, and R represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a cyano group or a halogen atom.
(4) The positive photoresist as described in the above (1), (2) or (3), wherein the above resin (A), (A1) or (A2) further contains a repeating unit represented by the following general formula (NIII), 
wherein Z1 represents xe2x80x94Oxe2x80x94 or xe2x80x94N(Rn6)xe2x80x94, wherein Rn6 represents a hydrogen atom, an alkyl group, a haloalkyl group, a hydroxyl group or xe2x80x94OSO2xe2x80x94Rn7, and Rn, represents an alkyl group, a haloalkyl group, a cycloalkyl group or a camphor residue.
(5) The positive photoresist as described in the above (1), (2) or (3), which further comprises (C) an organic basic compound and (D) a fluorine-type and/or silicon-type surfactant.